The present invention relates to a rotor blade for a wind turbine, in particular to a rotor blade having a variable dimension. It further relates to a wind turbine comprising the rotor blade, and to a method of controlling a wind turbine.
Wind turbines are commonly used to convert kinetic energy of an air stream into electric energy. An essential part of a wind turbine is the rotor with rotor blades, which captures the kinetic energy and converts it into rotational energy. Under normal wind conditions, it is generally desired to maximize the energy conversion efficiency. The efficiency of uptake of kinetic energy mainly depends on the aerodynamic profile and the pitch angle of the rotor blades. In order to adjust the pitch angle, the rotor blades can be rotated around their longitudinal axis by using a pitch drive. High-wind areas being limited, it is desired to use wind energy also under generally lower wind conditions. In order to extract sufficient wind energy under these conditions, it is desired to have a large blade size.
At very high wind speeds or gusts, however, the power captured from the wind by the rotor may exceed the limits set by the wind turbine's structural strength, especially for large blade sizes. Additionally, the generator's allowable maximum power constitutes a limit for the rotor's output power. Further, varying wind speed leads to a non-uniform rotation of the rotor and thereby creating additional non-uniform load. It is therefore a desire to reduce extreme loads at high wind speeds.
There is therefore a need for a rotor blade that can be flexibly adapted to various wind conditions.